I would never buy much there, because their prices are out of sight, but Market Garden is on the corner of Billy Folly Road and they are open until I think 9 PM every day. They have ample supplies for a first day, until you can get to Carrefour. The other option in Simpson Bay area is the Maho Market, in, wait for it--Maho. Not a store that has a big selection, and prices are relatively high, but good enough for first day supplies.